“…The rearrangement of 1 to 2 was not unexpected, as it closely resembles the known isomerization of biphenylene ( 4 ) to benzo[ a ]pentalene ( 5 ) . That skeletal reorganization can be viewed as a simple example of the well-known benzene ring contraction rearrangement, driven by relief of strain in the four-membered ring (Scheme ). 2 …”
mentioning
confidence: 58%
“…In an effort to uncover the simplest possible (nondegenerate) thermal migration of a phenyl group around the perimeter of a PAH diradical, we chose to examine the flash vacuum pyrolysis (FVP) of benzo[ b ]biphenylene ( 1 ) . At temperatures above 900 °C in the gas phase, two principal products are formed: indeno[2,1- a ]indene ( 2 ) and fluoranthene ( 3 ) (Scheme ). , The ratio of products 2 to 3 is 7:3 at 900 °C and 3:7 at 1100 °C. , Thus, isomerization to 2 is clearly favored at lower temperatures, but the pathway leading to 3 becomes dominant at higher temperatures. 1 …”
Flash vacuum pyrolysis of benzo[b]biphenylene, an alternant polycyclic aromatic hydrocarbon (PAH), gives fluoranthene, a nonalternant PAH, as the major product at 1100 degrees C in the gas phase. The most reasonable mechanism to explain this isomerization involves equilibrating diradicals of 2-phenylnaphthalene that rearrange by the net migration of a phenyl group to give equilibrating diradicals of 1-phenylnaphthalene, one isomer of which then cyclizes to fluoranthene.
“…The rearrangement of 1 to 2 was not unexpected, as it closely resembles the known isomerization of biphenylene ( 4 ) to benzo[ a ]pentalene ( 5 ) . That skeletal reorganization can be viewed as a simple example of the well-known benzene ring contraction rearrangement, driven by relief of strain in the four-membered ring (Scheme ). 2 …”
mentioning
confidence: 58%
“…In an effort to uncover the simplest possible (nondegenerate) thermal migration of a phenyl group around the perimeter of a PAH diradical, we chose to examine the flash vacuum pyrolysis (FVP) of benzo[ b ]biphenylene ( 1 ) . At temperatures above 900 °C in the gas phase, two principal products are formed: indeno[2,1- a ]indene ( 2 ) and fluoranthene ( 3 ) (Scheme ). , The ratio of products 2 to 3 is 7:3 at 900 °C and 3:7 at 1100 °C. , Thus, isomerization to 2 is clearly favored at lower temperatures, but the pathway leading to 3 becomes dominant at higher temperatures. 1 …”
Flash vacuum pyrolysis of benzo[b]biphenylene, an alternant polycyclic aromatic hydrocarbon (PAH), gives fluoranthene, a nonalternant PAH, as the major product at 1100 degrees C in the gas phase. The most reasonable mechanism to explain this isomerization involves equilibrating diradicals of 2-phenylnaphthalene that rearrange by the net migration of a phenyl group to give equilibrating diradicals of 1-phenylnaphthalene, one isomer of which then cyclizes to fluoranthene.
“…Flash vacuum pyrolysis of diphenylbutadiyne ( 5 ) gives indeno[2,1- a ]indene ( 6 ) in 19% yield by an ethyne−ethylidene rearrangement of alkynes . Indeno[2,1- a ]indenes have been synthesized by the nucleophilic substitution of bromine from tetrabromodibenzo[ a , e ]cyclooctene by organolithium reagents .…”
mentioning
confidence: 99%
“…Flash vacuum pyrolysis of diphenylbutadiyne (5) gives indeno[2,1-a]indene (6) in 19% yield by an ethyne-ethylidene rearrangement of alkynes. 7 Indeno[2,1-a]indenes have been synthesized by the nucleophilic substitution of bromine from tetrabromodibenzo[a,e]cyclooctene by organolithium reagents. 8 It has been reported that substitution with bulky groups 9 or benzofusion 10,11 gives stability to the pentalene framework.…”
mentioning
confidence: 99%
“…Here we present the unusual formation of the benzocyclyne dimer (10) and the indeno[2,1-a]indene derivative (11) under the conditions of the Sonogashira-Hagihara reaction (Scheme 1). Desilylation of 3-iodo-5,6-dimethyl-2-(2-(trimethylsilyl)ethynyl)hydroquinone (7) 12 by potassium fluoride in methanol gives 5,6-dimethyl-2-ethynyl-3-iodohydroquinone (8) in 63% yield. The combination of 8 with tert-butyldimethylsilyl chloride 13 and imidazole in dry methylene chloride under argon at room temperature for 2 days gives 5,6-dimethyl-2-ethynyl-3-iodo-1,4-bis-[((1,1-dimethylethyl)dimethylsilyl)oxy]benzene (9) in 43% yield.…”
The discovery of the equilibration of alkynes with ylidenecarbenes at high temperatures has been followed by increasing use of the reactivity of such carbenes in the synthesis of polycyclic aromatic hydrocarbons. This has led to simple and elegant syntheses of fullerene fragments, and of cyclopenta‐fused hydrocarbons. The related high‐temperature equilibration of arynes with ring‐contracted exocyclic carbenes has provided a further pathway for the transformation of polycyclic aromatic systems into less accessible cyclopenta‐fused hydrocarbons. Some recent developments in the chemistry of aryl radicals have extended the scope of radical approaches to the synthesis of polycyclic hydrocarbons.
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